1. Field of the Invention
The invention relates to a radial pneumatic tire and more specifically to an improved run-flat tire and method of assembling the run-flat tire during the manufacturing processes.
2. Description of the Prior Art
There is an ongoing effort by automobile manufacturers to eliminate the spare tire in order to reduce vehicle curb weight, increase available space within the vehicle and provide operator convenience. This is particularly true for vehicles having higher comfort specifications such as conventional luxury, family or urban-economy type vehicles. This effort has resulted in the development of pneumatic tires that are able to function for a limited time and distance at zero or near-zero inflation pressure, or commonly referred to as "run-flat" tires.
Run-flat tires have certain advantages over standard tires not designed to allow the vehicle to continue running with a loss of inflation pressure. Some of these advantages are follows:
1) It allows the driver the opportunity to find a more convenient time and location to change the flat tire. PA1 2) It enhances the handling of the vehicle with sudden loss of inflation pressure. PA1 3) It allows the driver the ability to avoid hazardous roadside situations. PA1 4) The robust sidewalls increase the tire's resistance to puncture/rupture from road hazards (i.e., scrap metal, potholes) and curb impact.
Numerous variations of run-flat tires have been developed. These involve changes to the structure of the tire itself and modifications to the rim to hold and support the flat tire. Each variation is limited by safety restrictions on vehicle speed, length of travel, zero inflation pressure handling and the magnitude of the lateral accelerations that force the bead of the tire off the rim seat. Further, the best solutions are those which do not affect the vehicle's nominal performance. The inflated ride comfort and handling should not be compromised by the design of the run-flat tire. Therefore, the need for improvements in the design of run-flat tires continues.
A number of run-flat tire designs have been disclosed which yield acceptable and sometimes improved vehicle/tire performance. These design features include thickened tire sidewalls, sidewall reinforcing plies, tire bead seat and vehicle rim configuration modifications, tire sidewall to rim flange contact improvements and tire belt package edge modifications. Each of these features can be used to help improve run-flat performance. One successful design feature of run-flat tires is thickened sidewalls to support the vehicle after loss of inflation pressure. Such a thickened sidewall, as the tire is viewed in cross-section, has a plurality of crescent-shaped reinforcing members of rubber in the tire's sidewall. These reinforcing members are interposed in each sidewall along with or between a plurality of carcass layers. With a loss of the inflation pressure in the tire, the crescent-shaped reinforcing members combine with the carcass layers to prevent collapse of the tire's sidewall so that the tire can effectively support the vehicle using its reinforced sidewalls.
A number of patents disclose a thickened sidewall design feature including a plurality of reinforcing members and a plurality of carcass layers. These include U.S. Pat. Nos. 5,238,040; 5,368,082; 5,427,166; and 5,511,599, and European Patent (EP) No. 385,192.
In U.S. Pat. No. 5,238,040 three reinforcement inserts are interposed between first and second carcass plies. A third textile reinforcing strip to the inside of the thickened sidewall portion extends from the crown area of the tire to a mid-height of the sidewall. The third strip reduces possible rubbing friction to increase the time for the tire to fail due to temperature and crushing conditions.
The disclosure of U.S. Pat. No. 5,368,082 describes a run-flat tire with elastomeric first and second fillers and a carcass reinforcing structure with two plies from bead to bead having turnup ends wrapped around each bead. The second filler is between the first and second carcass plies. The turnup ends terminate in radial proximity of the maximum section width of the tire. A special flat base bead core keeps the tire seated on a rim after the difficulty in mounting the tire on the rim has been overcome.
The disclosures of U.S. Pat. Nos. 5,427,166 and 5,511,599 both include three carcass layers extending from bead to bead. A middle carcass layer has turned up portions around each bead core and is interposed between first and second crescent-shaped reinforcing members in each sidewall. A third reinforcing member is disclosed in U.S. Pat. No. 5,511,599 to extend radially outward from and contiguous with a bead filler.
In EP 385,192 a lenticular (crescent-shaped) section member disposed at the inside of the sidewall has a textile reinforcement insert. The insert divides the lenticular section member and extends radially outward from a side center line to as far as under the end of the belt. In another embodiment the insert extends from one end radially outward of a bead filler in one sidewall to the other end in a similar location in the other sidewall.
The manufacturing of run-flat tires having reinforced sidewalls involves the assembly of a large number of components when compared to a tire with no sidewall reinforcing members. The addition of crescent-shaped reinforcing members disposed with a plurality of carcass layers becomes very difficult and time consuming during the tire building process, especially when laying components on a tire building drum. In addition, carcass layers generally extend from bead to bead and may encircle the bead to wrap around the bead core and extend radially outward into the sidewall. These carcass layers result in further time delays and complexity in the building run-flat tires. A need exists to simplify the run-flat tire and the tire manufacturing process to maintain productivity at generally acceptable levels.
Tires with reinforced sidewalls as previously discussed may be simplified by truncating carcass layers in either or both the bead area and the crown area of the tire to provide partial. Typical patents which illustrate partial carcass layers include U.S. Pat. Nos. 4,067,372; 4,287,924; 5,164,029; 5,217,549; and 5,361,820, European Patent No. 385,192 and Japanese (JP) Patent No. 3-143710.
U.S. Pat. No. 4,067,374 discloses the use of a crescent-shaped sidewall reinforcing rubber portion positioned to the inside of partial carcass layers. The crescent-shape sidewall reinforcing member is put into compression while the cords of the partial carcass layers are put into tension with the loss of inflation pressure in the tire; thereby inhibiting collapse of the sidewall. The partial carcass layers each extend from a respective bead core to overlap the lateral edges of the belt. Partial carcass layers are formed by incorporating reinforcing fibers in a rubbery mixture. The other carcass layer is located to the inside of the reinforcing member and extends from bead to bead and is wrapped around each bead. This carcass layer would also be in tension with the loss of inflation pressure.
In U.S. Pat. No. 4,287,924 a two part crescent-shaped member has a heat conducting sheet or layer between the two parts. The layer extends over the whole height of the crescent-shaped portions and the two crescent-shaped parts are of different flexibility. The heat conducting layer may have parallel metallic cords extending radially to assist in the heat conductivity. The height of the disclosed tire of this patent is only 31 percent of its inflated height when the inflation pressure is zero.
In U.S. Pat. No. 5,164,029 carcass reinforcing layers are disposed on either one or both sides of a carcass. Reinforcing layers are partial layers extending from a lapping arrangement with the belt edge to a location outward of the bead core. A two component bead apex is further disclosed having a stiffener portion made of hard rubber and a buffer portion. The reinforcing layers and the bead apex help support the tire by increasing lateral and vertical spring coefficients of the tire. The tire of this patent improves the tire's vibration performance and provides only limited self supporting capability.
The pair of crescent-shaped elastomeric reinforcing members disclosed in U.S. Pat. No. 5,217,549 are preferably for high profile tires having a section height of 5 inches (127 millimeters) or greater. Sidewall stiffness is achieved by a single high modulus crescent-shaped reinforcing member in each sidewall to the inside of two carcass plies and a reinforced bias ply adjacent to the two carcass plies. The bias ply extends radially inward from each lateral edge of the belt to a location radially outward of the bead core and are bias at an angle of 60 degrees.
The radial tire disclosed in U.S. Pat. No. 5,361,820 includes a carcass layer composed of a single ply of carcass cords folded up around the bead core to an radial outward position below the belts. A hard rubber layer is disposed between the carcass layer and the folded-up portion to insure a high lateral spring constant to maintain good maneuverability. The tire of this patent has an improved production rate and a reduced tire weight when compared to other tires with a high lateral spring constant.
In EP 385,192 a textile reinforcement insert is positioned in the crown area of the tire and extends radially inward to divide a crescent-shaped reinforcing member. The insert stops at a distance radially outward of the bead core beyond the apex of the bead filler. The insert lies along the center axis of the crescent-shaped member. The crescent-shaped member also terminates at the radial outermost extent of the bead filler in this patent.
A cord reinforcing unit on the interior surface of the crescent-shaped reinforcing member in JP 3-143710 consists of at least one reinforced ply. The reinforcing member is to the inside of two carcass plies which wrap around the bead core. The inner reinforcing unit extends outward from a location above the bead core to a lapping arrangement with the belt layer. The reinforcing member and the reinforcing unit provides the overall sidewall support for run-flat performance. Only one crescent-shaped reinforcing member is illustrated.
Efforts to reduce the production time for building tires by improving the tire assembly processes are disclosed in U.S. Pat. Nos. 4,875,959; 5,088,539; 5,267,595; and 5,215,612. Improvements include forming methods for components of the tire, combining sidewall components and the efficient assembly of products on a tire building drum.
In U.S. Pat. No. 4,875,050 a tire forming method is disclosed for piling tire forming members one on another with their ends shifted to form a member assembly. Three separate components are formed, cut to length and joined together with high accuracy. The tire members thus joined together can be formed on a winding roller.
Sidewalls of the tire disclosed in U.S. Pat. No. 5,267,595 each have a two-layer structure disposed on the lateral outer sides of the carcass which extend from the bead rubber members to shoulder regions of the tire. The patent of U.S. Pat. No. 5,088,537 discloses a sidewall having a three-layer structure extending from the bead area to the tread. Each rubber layer can be made with different materials for the different performance criteria of the tire's sidewall. If one would consider the sidewall to have a single structure, instead of two or three separate components or layers in tire building process, the building of the tire could be simplified.
A typical method for manufacturing tires is illustrated and disclosed in U.S. Pat. No. 5,215,612. Portions of a green tire are assembled or formed by wrapping uncured tire components around a forming or tire building drum. A plurality of pieces or components are placed at both lateral sides of a continuous carcass ply which is subsequently wrapped around a bead core. In U.S. Pat. No. 5,215,612 the importance of bonding rubber pieces on the end of a sidewall rubber portions in building the tire is disclosed. This method becomes essential in reducing the tire's production time when a large number of sidewall components are present in the formation of the green tire on a building drum.
The references fail to teach how to improve the production time of a run-flat tire having a plurality of crescent-shaped reinforcing members and carcass layers. A desirable production capacity would be the ability to produce a run-flat tire having sidewall supporting capabilities in approximately the same time as a standard tire having no sidewall supporting capability. Tire manufacturing plants must be able to produce enough tires to meet the constant demand for tires that exists.
In accordance with the limitations of the references, one object of the present invention is to provide a simplified method for manufacturing run-flat tires having self supporting sidewalls with little change in production capability.
A further object of this invention is to provide a run-flat tire having sidewall components and carcass layers which result in a run-flat tire which can be easily manufactured. This run-flat tire is to include a reduction in the extent of components provided to make a run-flat tire without compromising the performance of the tire.
Another object of this invention is to provide a run-flat tire which can be constructed by conventional manufacturing techniques, requiring few additional manufacturing steps and procedures. Conventional manufacturing techniques are used to provide a cost effective run-flat tire produced at an improved rate of production when compared to present production rates for run-flat tires.